Witnesses of NZ shooting fled amid bodies

People who were inside a Christchurch mosque when a gunman opened fire have described scenes of death as world leaders condemn the man behind one of New Zealand's "darkest days".

New Zealand Prime Minister Jacinda Ardern said dozens of people died in the "act of extreme violence".

"It is clear that this can now only be described as a terrorist attack," she said on Friday.

"This is one of New Zealand's darkest days."

Syed Ahmed was among those worshipping at a mosque on the New Zealand city's Linwood Avenue on Friday afternoon when he says a man wearing a black motorcycle helmet and camouflage clothing begin shooting from outside.

Mr Ahmed has told the news site Stuff he believes at least eight people were shot, the first being elderly people sitting on chairs as they prayed.

"They were basically all shot," he said.

The shooter was "shouting something", which Mr Ahmed couldn't hear over the sound of screams, before he crawled into a storeroom to escape the carnage.

The attacker is believed to be 28-year-old Australian man Brenton Tarrant, who is now charged with murder.

Sabir Hussain told Stuff he was praying at the same mosque when he heard the imam (leader of the mosque) say "our brothers have been shot".

He went into the washroom where he saw a man dead outside, prompting him to jump out a window and hide behind a fence until police arrived.

The Linwood Avenue mosque is one of two allegedly targeted by Tarrant, with another taking place at a mosque on Deans Avenue.

Len Peneha, who lives next door to the latter, told the Associated Press he saw a man dressed in black enter the mosque at about 1.45pm.

He then heard dozens of shots as people ran out in terror and went into the mosque to help.

"I saw dead people everywhere. There were three in the hallway, at the door leading into the mosque, and people inside the mosque," he said.

Another man, Farid Ahmed, told reporters how he pushed his wheelchair into the back car park of the mosque in a desperate attempt to save himself.

"From there I was hearing shooting after shooting after shooting," he said.

"I could hear screaming and crying, I saw some people drop dead."

"I could not go anywhere and I didn't want to, I was afraid what would happen to the ladies (in the mosque) and what would happen to my wife."

The death toll stands at 49.

Two other men and a woman have been arrested, their involvement is unclear.

Tarrant and the other people arrested were not on police watch lists either in New Zealand or Australia.